Wash and dry the cherries. Pit them over a bowl, reserving all flesh and juices. If you really like cooking and baking with cherries, it really is worth it to buy a cherry pitter. I'm not one for single use kitchen gadgets, but it really does the job. If not, just halve the cherries and remove the pit.,Whisk together the sugar and cornstarch in a bowl. In a large pot, whisk together the water and lemon juice, then add the sugar and cornstarch in, whisking well to combine and remove any lumps. Bring the mixture to a boil.,______,Ladle the mixture into sanitized canning jars, leaving 1 inch of headspace. Fasten the lids to each jar, and transfer to a boiling water canner. Process for 30 minutes, then remove and let cool completely at room temperature. Check the seals, then store in a cool, dark place.